Calcium-rich biochar from crab shell: An unexpected super adsorbent for dye removal

Preparation of silver-based metal-organic framework and chitosan hybrid material for removing drug and dye

Pharmaceuticals and personal care products and dyes have low biodegradability and high toxicity, seriously threaten the human health and ecological environment. Therefore, seeking effective removal methods has become the focus of research. In this study, silver-based metal-organic framework (Ag-MOF) and chitosan (CS) hybrid adsorbent (Ag-MOF-CS) was synthesized via solvothermal one-pot synthesis to remove diclofenac sodium (DCF) and acid Red 1 (AR1) from water for the first time. The morphology and structure of Ag-MOF-CS were confirmed by various characterizations. The effect on adsorption was investigated by changing the adsorbent dosage, pH and other conditions. The adsorption kinetics, adsorption isotherms and thermodynamics were analyzed. Ag-MOF-CS showed a high adsorption capacity. And the maximum adsorption capacity of Ag-MOF-CS for DCF and AR1 was 351.75 mg/g and 678.83 mg/g, respectively. The adsorbent bound to DCF and AR1 may via electrostatic forces, π-π interactions, hydrogen bonding. Even after four cycles of Ag-MOF-CS, the DCF removal can still be higher than 80 %. The eco-friendly Ag-MOF-CS demonstrated significant potential for utilization in treating wastewater.

Recent approaches and advancement in biochar-based environmental sustainability: Is biochar fulfilling the sustainable development goals?

This review highlights the application of biochar (BC) for attaining different SDGs (SDG 6: clean water and sanitation, SDG 7: affordable and clean energy, SDG 13: climate action, and SDG 15: life on land). These goals coincide with the various existing environmental problems including wastewater treatment, soil amendment, greenhouse gas remediation, and bioenergy generation. So, the review encompasses the various mechanisms involved in the BC-assisted treatment and reclamation of water, pollutant immobilization and enhancing soil properties, reduction of greenhouse gas emission during the wastewater treatment process and soil amendment mechanisms, bioenergy generation through various electrode material, biodiesel production, and many more. The review also explains the various drawbacks and limitations of BC application to the available environmental issues. Conclusively, it was apprehended that BC is an appropriate material for several environmental applications. More research interventions are further required to analyze the applicability of different BC materials for attaining other available SDGs.

A statistical optimization for almost-complete methylene blue biosorption by Gracilaria bursa-pastoris

In this study, the dried biomass of four marine algae, namely Porphyra sp., Gracilaria bursa-pastoris, Undaria pinnatifida and Laminaria sp., were screened for their ability to remove methylene blue (MB) dye from aqueous solutions. Statistical approaches of the Plackett-Burman Design (PBD) and Box-Behnken Design (BBD) were applied to optimize different environmental conditions in order to achieve the maximum MB removal percentage by Gracilaria bursa-pastoris. The biosorbent was characterized before and after adsorption process using FTIR, XRD and SEM analysis. Additionally, isotherms, kinetics and thermodynamics studies were conducted to investigate the adsorption behavior of the adsorbent. The results showed that Gracilaria bursa-pastoris achieved the highest dye removal efficiency (98.5 %) compared to 96.5 %, 93.5 % and 93.9 % for Undaria pinnatifida, Porphyra sp. and Laminaria sp., respectively. PBD analysis revealed that the agitation speed, pH, and biomass dose were found to be the significant parameters affecting MB removal onto Gracilaria dried biomass. According to the BBD results, the maximum dye removal percentage (99.68 %) was obtained at agitation speed of 132 rpm, pH 7 and biomass dose of 7.5 g/L. FTIR, XRD and SEM analysis demonstrated the participation of several functional groups in the adsorption process and changes in the cell surface morphology of the adsorbent following the dye adsorption. The adsorption isotherms showed better fit to Freundlich model (R2 = 0.9891) than the Langmuir, Temkin, and Dubinin-Radushkevich models. The adsorption kinetics were best described by the pseudo-second-order model (R2 = 0.9999), suggesting the chemical interactions between dye ions and the algal biomass. The thermodynamic parameters indicated that the adsorption of MB onto Gracilaria dried biomass was spontaneous, feasible, endothermic and random. These results indicate that dried biomass of Gracilaria bursa-pastoris is an attractive, environmentally friendly, cheap and effective agent for MB dye removal from environmental discharges.

Machine learning screening of biomass precursors to prepare biomass carbon for organic wastewater purification: A review

In the past decades, the amount of biomass waste has continuously increased in human living environments, and it has attracted more and more attention. Biomass is regarded as the most high-quality and cost-effective precursor material for the preparation carbon of adsorbents and catalysts. The application of biomass carbon has extensively explored. The efficient application of biomass carbon in organic wastewater purification were reviewed. With briefly introducing biomass types, the latest progress of Machine learning in guiding the preparation and application of biomass carbon was emphasized. The key factors in constructing efficient biomass carbon for adsorption and catalytic applications were discussed. Based on the functional groups, rich pore structure and active site of biomass carbon, it exhibits high efficiency in water purification performance in the fields of adsorption and catalysis. In addition, out of a firm belief in the enormous potential of biomass carbon, the remaining challenges and future research directions were discussed.

Synthesis of a novel magnetic calcium-rich biochar nanocomposite for efficient removal of phosphate from aqueous solution

Phosphorus (P) scarcity and eutrophication have triggered the development of new materials for P recovery. In this work, a novel magnetic calcium-rich biochar nanocomposite (MCRB) was prepared through co-precipitation of crab shell derived biochar, Fe2+ and Fe3+. Characteristics of the material demonstrated that the MCRB was rich in calcite and that the Fe3O4 NPs with a diameter range of 18-22 nanometers were uniformly adhered on the biochar surface by strong ether linking (C-O-Fe). Batch tests demonstrated that the removal of P was pH dependent with an optimal pH of 3-7. The MCRB exhibited a superior P removal performance, with a maximum removal capacity of 105.6 mg g-1, which was even higher than the majority lanthanum containing compounds. Study of the removal mechanisms revealed that the P removal by MCRB involved the formation of hydroxyapatite (HAP-Ca5(PO4)3OH), electrostatic attraction and ligand exchange. The recyclability test demonstrated that a certain level (approximately 60%) was still maintained even after the six adsorption-desorption process, suggesting that MCRB is a promising material for P removal from wastewater.

A critical review on biochar for the removal of toxic pollutants from water environment

As an effort to tackle some of the most pressing ecological issues we are currently experiencing, there has been an increasing interest in employing biomass-derived char products in various disciplines. Thermal combustion of biomass results in biochar production, which is a remarkably rich source of carbon. Not only does the biochar obtained by the thermochemical breakdown of biomass lower the quantity of carbon released into the environment, but it also serves as an eco-friendly substitute for activated carbon (AC) and further carbon-containing products. An overview of using biochar to remove toxic pollutants is the main subject of this article. Several techniques for producing biochar have been explored. The most popular processes for producing biochar are hydrothermal carbonization, gasification and pyrolysis. Carbonaceous materials, alkali, acid and steam are all capable of altering biochar. Depending on the environmental domains of applications, several modification techniques are chosen. The current findings on characterization and potential applications of biochar are compiled in this survey. Comprehensive discussion is given on the fundamentals regarding the formation of biochar. Process variables influencing the yield of biochar have been summarized. Several biochars' adsorption capabilities for expulsion pollutants under various operating circumstances are compiled. In the domain of developing biochar, a few suggestions for future study have been given.

Mechanisms for synergistically enhancing cadmium remediation performance of biochar: Silicon activation and functional group effects

This work proposes an advanced biochar material (β-CD@SiBC) for controllable transformation of specific silicon (Si) forms through endogenous Si activation and functional group introduction for efficient cadmium (Cd) immobilization and removal. The maximum adsorption capacity of β-CD@SiBC for Cd(II) reached 137.6 mg g-1 with a remarkable removal efficiency of 99 % for 200 mg L-1Cd(II). Moreover, the developed β-CD@SiBC flow column exhibited excellent performance at the environmental Cd concentration, with the final concentration meeting the environmental standard for surface water quality (0.05 mg L-1). The remediation mechanism of β-CD@SiBC could be mainly attributed to mineral precipitation and ion exchange, which accounted for 42 % and 29 % of the remediation effect, respectively, while functional group introduction enhanced its binding stability with Cd. Overall, this work proposes the role and principle of transformation of Si forms within biochar, providing new strategies for better utilizing endogenous components in biomass.

Structural properties and adsorption performance relationship towards three categories of lignin and their derived biochar

The growing interest in utilizing lignin for dye removal has gained momentum, but there is limited information on the intricate relationship between lignin structural characteristics and adsorption efficacy, especially for its biochar derivatives. This study focused on three types of lignin and their corresponding biochar derivatives. Among them, ZnCl2-activated acidic/alkali densified lignin preparation of lignin-derived active carbon exhibited superior adsorption performance, achieving 526.32 mg/g for methylene blue and 2156.77 mg/g for congo red. Its exceptional adsorption capacity was attributed to its unique structural properties, including low alkyl and O-alkyl group content and high aromatic carbon levels. Furthermore, the adsorption mechanisms adhered to pseudo-second-order kinetics and the Langmuir model, signifying a spontaneous process. Intriguingly, lignin-derived active carbon also demonstrated remarkable recovery capabilities. These findings provide valuable insights into the impact of structural attributes on lignin and its biochar's adsorption performance.

Upcycling crab shell waste into biochar for treatment of palm oil mill effluent via microwave pyrolysis and activation

The escalating consumer demand for crabs results in a growing amount of waste, including shells, claws, and other non-edible parts. The resulting crab shell waste (CSW) is disposed of via incineration or landfills which causes environmental pollution. CSW represents a potential biological resource that can be transformed into valuable resources via pyrolysis technique. In this study, microwave pyrolysis of CSW using self-purging, vacuum, and steam activation techniques was examined to determine the biochar production yield and its performance in treating palm oil mill effluent (POME). The biochar produced through microwave pyrolysis exhibits yields ranging from 50 to 61 wt%, showing a hard texture, low volatile matter content (≤34.1 wt%), and high fixed carbon content (≥58.3 wt%). The KOH-activated biochar demonstrated a surface area of up to 177 m2/g that is predominantly composed of mesopores, providing a good amount of adsorption sites for use as adsorbent. The biochar activated with steam removed 8.3 mg/g of BOD and 42 mg/g of COD from POME. The results demonstrate that microwave pyrolysis of CSW is a promising technology to produce high-quality biochar as an adsorbent for POME treatment.

Thermally modified nanocrystalline snail shell adsorbent for methylene blue sequestration: equilibrium, kinetic, thermodynamic, artificial intelligence, and DFT studies

In recent years, the quest for an efficient and sustainable adsorbent material that can effectively remove harmful and hazardous dyes from industrial effluent has become more intense. The goal is to explore the capability of thermally modified nanocrystalline snail shells (TMNSS) as a new biosorbent for removing methylene blue (MB) dye from contaminated wastewater. TMNSS was employed in batch adsorption experiments to remove MB dye from its solutions, taking into account various adsorption parameters such as contact time, temperature, pH, adsorbent dosage, and initial concentration. SEM, EDS, XRD, and FTIR were used to characterize the adsorbent. The study further developed and adopted adaptive neuro-fuzzy inference system (ANFIS) and density functional theory (DFT) studies to holistically examine the adsorption process of MB onto the adsorbent. EDX and FTIR confirm the formation of CaO with a sharp peak at 547 cm-1, and C-O and O-H are present, as well. SEM and XRD show an irregularly shaped highly crystalline nanosized (65 ± 2.81 nm) particle with a lattice parameter value of 8.611617 Å. The adsorption efficiency of 96.48 ± 0.58% was recorded with a pH of 3.0 and an adsorbent dose of 10 mg at 30 °C. The findings from the study fit nicely onto Freundlich isotherms, with Qm = 31.7853 mg g-1 and R2 = 0.9985. Pseudo-second-order kinetics recorded the least error value of 0.8792 and R2 = 0.9868, thus indicating chemisorption and multilayer adsorption processes. The exothermic and spontaneous nature of the adsorption process are demonstrated by ΔH° and ΔG°. The performance of the ANFIS-based prediction of removal rate, which was demonstrated by a root mean square error (RMSE) value of 2.2077, mean absolute deviation (MAD) value of 1.1429, mean absolute error (MAE) value of 1.8786, and mean absolute percentage error (MAPE) value of 2.0178, revealed that the ANFIS model predictions and experimental findings are in good agreement. More so, DFT provides insights into the molecular interactions between MB and the adsorbent surface, with a calculated adsorbate-adsorbent binding affinity value of -1.3 kcal mol-1, thus confirming the ability of TMNSS for MB sequestration. The findings of this study highlight the promising potential of thermally modified nanocrystalline snail shells as sustainable and efficient adsorbents for MB sequestration.

Norfloxacin adsorption by urban green waste biochar: characterization, kinetics, and mechanisms

Biochar, as a potential adsorbent, has been widely employed to remove pollutants from sewage. In this study, a lignin-based biochar (CB-800) was prepared by a simple high-temperature pyrolysis using urban green waste (Cinnamomum camphora leaves) as a feedstock to remove norfloxacin (NOR) from water. Batch adsorption test results indicated that CB-800 had a strong removal capacity for NOR at a wide range of pH values. The maximum adsorption achieved in the study was 50.90 ± 0.64 mg/g at 298 K. The pseudo-first and second-order kinetic models and the Dubinin-Radushkevich isotherm fitted the experimental data well, indicating that NOR adsorption by CB-800 was a complex process involving both physi-sorption and chemi-sorption. The physical properties of CB-800 were characterized by SEM and BET. The mesoporous structures were formed hierarchically on the surface of CB-800 (with an average pore size of 2.760 nm), and the spatial structure of NOR molecules was more easily adsorbed by mesoporous structures. Combined with Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis, it was showed that the main NOR adsorption mechanisms by CB-800 included ion exchange, π-electron coordination, hydrogen bonding, and electrostatic adsorption. Meanwhile, the reduction of C = O and pyridine nitrogen, and the presence of C-F2, also indicated the occurrence of substitution, addition, and redox. This study not only determined the reaction mechanism between biochar and NOR, but also provides guidance to waste managers for the removal of NOR from water by biochar. It is envisaged that the results will broaden the utilization of urban green waste.

Chitin/calcite composite extracted from shell waste as a low-cost adsorbent for removal of tetracycline and ciprofloxacin: Effects and mechanisms

Recently, water contamination caused by the misuse of antibiotics has become a growing concern. In this study, an economical chitin/calcite composite (CCA) was extracted from crab shell waste, and the effects and mechanisms of its removal of ciprofloxacin (CIP) and tetracycline (TC) from aqueous solution were investigated. The functional groups of chitin and the metal phase of calcite gave CCA the ability to remove antibiotics. Experiments on kinetics, isothermal adsorption, thermodynamics, co-removal, and reusability were conducted to systematically explore the adsorption performances of CCA toward antibiotics. The pseudo-second-order (FSO) and Langmuir models suited the data obtained from experiments best and displayed a good fit for the chemisorption and a certain homogeneity of adsorption sites. At 25 °C, the maximum adsorption capacities (Qmax) toward CIP and TC were 228.86 and 150.76 mg g-1, respectively. The adsorption mechanisms of CCA with TC and CIP are pH dependent since pH can affect the surface charge of CCA and the form in which CIP and TC are existing. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) demonstrated that the keto-O and carboxyl groups of CIP and the carbonyl, hydroxyl, and amido groups of TC could be responsible for the binding with the calcite and the functional groups of chitin through surface complexation, cation bridge and hydrogen bonding.

Green construction of biochar@NiFe2O4 nanocomposite for highly efficient photocatalytic remediation of pesticides from agriculture wastewater

The world's attention is drawn to the widespread ingestion, toxicity, and bioaccumulation of the Atrazine (AT) and Endosulfan (ES). Pesticides have been proven to have endocrine-disrupting, genotoxic, and persistent characteristics. In this work, the structural design of green synthesized NiFe2O4 is incorporated in rice husk biochar to form BC@NiFe2O4 nanocomposite. Powder X-ray diffraction and microscopic analysis confirmed the semi-crystalline nature of BC@NiFe2O4 reduced due to the incorporation of amorphous BC. The green BC@NiFe2O4 nanocomposite degraded AT and ES up to 98 % and 92 %, respectively. The maximum degradation achieved by BC@NiFe2O4 nanocomposite with minimum pollutants concentration (50 mg L-1) with 10 mg catalyst dose at acidic pH in natural sunlight because of the higher negative value of zeta potential (-26.4 mV) and lower band gap (2.5 eV). The degradation process involves first-order kinetics followed by initial Langmuir adsorption. The presence of various radical quenchers (t-BuOH, p-BZQ, Na2EDTA) has led to the conclusion that hydroxyl radicals play a significant role in the degradation of the toxic substances AT and ES. Additionally, a green-fabricated BC@NiFe2O4 nanocomposite has exhibited exceptional efficiency in degrading AT and ES pollutants in actual wastewater samples. Furthermore, this nanocomposite has demonstrated outstanding sustainability and cost-effectiveness, maintaining its effectiveness for up to eight cycles without a noticeable reduction in activity. In summary, due to its favorable surface characteristics, the environmentally friendly BC@NiFe2O4 nanocomposite holds excellent promise as a unique and potential photocatalyst for various industrial applications.

Sustainable use of low-cost adsorbents prepared from waste fruit peels for the removal of selected reactive and basic dyes found in wastewaters

Agricultural wastes are potential sustainable adsorbents since they are available in large quantities, are low-cost, and may require little or no treatment, in some cases. In this study, several fruit peels, such as banana, orange, and pomegranate, were collected from local markets and prepared by a simple and eco-friendly method and used as natural adsorbents for the removal of both anionic (Reactive Red 120 (RR120), Reactive Black 5 (RB5), Remazol Brilliant Blue R (RBBR)) and cationic Methylene Blue (MB) dyes found in wastewaters. Many industries, such as leather and textiles, can release huge amounts of synthetic dyes into the wastewater during dyeing processes. These are one of the most important pollutants of water pollution as they cause enormous damage to the water body and also affect the health of organisms due to their toxicity and carcinogenicity. The search for a sustainable and at the same time efficient material for the removal of a wide variety of dyes is the innovation of this work. These peels were prepared by washing, drying, grinding, and finally sieving, under natural sustainable conditions. Porosometry (BET analysis), FTIR, SEM/EDS, and XRD techniques were used to characterize the fruit peels before and after the adsorption process. Factors affecting the adsorption of dyes (adsorbent dosage, pH solution, initial concentration of dyes, contact time, and temperature) were investigated. According to the results, in terms of the effectiveness of fruit peels as (natural) adsorbent materials, for anionic dyes, 5.0-6.0 g/L of banana or orange dry peels was sufficient to remove near or even more than 90% anionic dyes at pH 2.0, and 4.0 g/L was sufficient to remove 98% of cationic MB dye at pH 9.0. Similar amount of pomegranate peels had lower efficiency for anionic dyes (50-70%), while cationic MB was still efficiently removed (98%) at pH 9.0. Moreover, the adsorption process in all cases was found to better fit to pseudo-second-order model, in comparison to pseudo-first-order model. According to isotherms, Freundlich model fitted better in some cases to the equilibrium data, while the Langmuir model in others. Finally, this study demonstrates the viability of reusing the banana, orange, and pomegranate peel adsorbents for eight, four, and five cycles, showing a gradual reduction of around 50% of their effectiveness.

A response surface model to examine the reactive red 239 sorption behaviors on Rhizoclonium hieroglyphicum: isotherms, kinetics, thermodynamics and toxicity analyses

The present study is an attempt to investigate the potentiality of Rhizoclonium hieroglyphicum in the removal of reactive red 239 (RR239) from aqueous solution and to assess the toxicity of the treated dye solution. Optimisation of the process variables namely dye and biosorbent concentrations, pH, temperature and incubation time for RR239 removal was performed using Response Surface Methodology (RSM) assisted Box Behnken Design (BBD) model. The recycling and regeneration efficiency of the dye adsorbed alga was evaluated using different eluents under optimized conditions. Further to understand the adsorption mechanism, isotherms, kinetics and thermodynamic studies were performed. UV-vis and FT-IR spectroscopy was employed to confirm the interaction between the adsorbate and biosorbent. The nature of the treated dye solution was assessed using phyto, microbial and brine shrimp toxicity studies. On the basis of quadratic polynomial equation and response surfaces given by RSM, 90% decolorization of RR239 was recorded at room temperature under specified optimal conditions (300 mg/L of dye, 500 mg/L of biosorbent, pH 8 and 72 h of contact time). Desorption experiments demonstrated 88% of RR239 recovery using 0.1 N acetic acid as an eluent and 81% of dye removal in regeneration studies. The data closely aligned with Freundlich isotherm (R2 - 0.98) and pseudo-second-order kinetic model (R2 - 0.9671). Thermodynamic analysis revealed that the process of adsorption was endothermic, spontaneous, and favorable. UV-Vis and FT-IR analyses provided evidence for adsorbate-biosorbent interaction, substantiating the process of decolorization. In addition, the results of phyto, microbial and brine shrimp toxicity assays consistently confirmed the non-toxic nature of the treated dye. Thus, the study demonstrated that R. hieroglyphicum can act as a potent bioremediation agent in alleviating the environmental repercussions of textile dyeing processes.

Simultaneous removal of phosphate and tetracycline using LaFeO3 functionalised magnetic biochar by obtained ultrasound-assisted sol-gel pyrolysis: Mechanisms and characterisation

Excessive phosphate and tetracycline (TC) contaminants pose a serious risk to human health and the ecological environment. As such exploring the simultaneous adsorption of phosphate and TC is garnering increasing attention. In this study, an efficient lanthanum ferrate magnetic biochar (FLBC) was synthesised from crab shells using an ultrasound-assisted sol-gel method to study its performance and mechanisms for phosphate and TC adsorption in aqueous solutions in mono/bis systems. According to the Langmuir model, the developed exhibited a maximum adsorption capacity of 65.62 mg/g for phosphate and 234.1 mg/g for TC (pH:7.0 ± 0.1, and 25 °C). Further, it exhibited high resistance to interference and pH suitability. In practical swine wastewater applications, whereby the concentrations of phosphate and TC are 37 and 19.97 mg/L, respectively, the proposed material demonstrated excellent performance. In addition, electrostatic adsorption, chemical precipitation and ligand exchange were noted to be the main mechanisms for phosphate adsorption by FLBC, whereas hydrogen bonding and π-π interaction were the main adsorption mechanisms for TC adsorption. Therefore, this study successfully prepared a novel and efficient adsorbent for phosphate and TC.

Enhanced adsorption of Congo red from urea/calcium chloride co-modified biochar: Performance, mechanisms and toxicity assessment

Adsorbents with excellent physicochemical properties and green synthetic routes are desired for efficient removal of Congo red (CR) wastewater. Hence, a novel approach was proposed within this work. Biochar NCBC obtained from Medulla Tetrapanacis was synthesized through co-modification with urea/calcium chloride. NCBC exhibited an enormous surface area (750.09 m2/g) and a micro-mesoporous composite structure. Higher nitrogen content was detected on the surface of NCBC (8.17%) compared to that of urea directly modified biochar (4.63%). Nitrogen observed on the surface of NCBC was presented as graphitic N, pyrrolic N, amine N as well as pyridinic N. Kinetic and isothermal investigations revealed the active sites on NCBC to be homogeneous and bind to CR mainly by chemisorption. Calculated maximum sorption of CR on NCBC was 2512.82 mg/g basing on Langmuir model. Moreover, the practicality of NCBC was further proved by the cultivation of Nelumbo nucifera Gaertn. and Penicillium.

Efficiency and selectivity of cost-effective Zn-MOF for dye removal, kinetic and thermodynamic approach

Green synthesis of metal-organic frameworks (MOFs) has attracted a lot of attention as a crucial step for practical industrial applications. In this work, green synthesis of zinc(II) metal-organic framework (Zn-MOF) has been carried out at room temperature. The Zn metal (node) was extracted from spent domestic batteries, and the linker was benzene di-carboxylic acid (BDC). The characterization of the as-prepared Zn-MOF was accomplished by PXRD, FT-IR spectroscopy, SEM, TEM, TGA, and nitrogen adsorption at 77 K. All the characterization techniques strongly supported that as-synthesized Zn-MOF using metallic solid waste Zn is similar to that was reported in the literature. The as-prepared Zn-MOF was stable in water for 24 h without any changes in its functional groups and framework. The prepared Zn-MOF was tested for the adsorption of three dyes, two anionic dyes, aniline blue (AB), and orange II (O(II)) as well as methylene blue (MB), an example of cationic dye from aqueous solution. AB has the highest equilibrium adsorbed amount, qe, of value 55.34 mg g-1 at pH = 7 and 25 °C within 40 min. Investigation of the adsorption kinetics indicated that these adsorption processes could be described as a pseudo-second-order kinetic model. Furthermore, the adsorption process of the three dyes was described well by the Freundlich isotherm model. According to the thermodynamic parameters, the adsorption of AB on the prepared Zn-MOF was an endothermic and spontaneous process. In contrast, it was non-spontaneous and exothermic for the uptake of O(II) and MB. This study complements the business case development model of "solid waste to value-added MOFs."

Substantial increase in adsorption efficiency of local clay-alginate beads toward methylene blue impregnated with SDS

In the current research work, local clay-alginate beads loaded with sodium dodecyl sulfate (SDS) surfactant were prepared for efficient adsorption of methylene blue (MB). FTIR, SEM-EDX, and TGA instruments were used to examine the surface functional groups, morphology, elemental analysis, and thermal stability of beads, respectively. The adsorption efficiency of native clay for MB increases from 124.78 to 247.94 mg/g when loaded in alginate and SDS in beads form. The impacts of adsorbent dosage, initial pH, contact time, initial MB concentration, and temperature were investigated and optimized. The maximum adsorption capacity of beads for MB was 1468.5 mg/g. The process followed a pseudosecond order kinetic and Freundlich adsorption isotherm model. Thermodynamic study confirmed that MB adsorption on beads is endothermic and spontaneous in nature. The beads were recycled and reused for five times. According to the findings, local clay-alginate beads impregnated with SDS proved to be a promising and efficient adsorbent for extracting MB from aqueous solution.

Functionalized biochars with highly-efficient malachite green adsorption property produced from banana peels via microwave-assisted pyrolysis

In this study, functionalized banana peel biochar (BPB) was prepared by microwave-assisted pyrolysis for the first time to investigate its adsorption to malachite green (MG) dye. Adsorption experiments showed that the maximum adsorption capacity of BPB500 and BPB900 to malachite green reached 1790.30 and 2297.83 mg·g^-1 within 120 min. The adsorption behaviour was well-fitted by the pseudo-second-order kinetic model and Langmuir isotherm model, and ΔG⁰ < 0, ΔH⁰ > 0, indicated that the adsorption process was endothermic and spontaneous, dominated by chemisorption. The adsorption mechanism of MG dye on BPB included hydrophobic interaction, hydrogen bonding, π-π interaction, n-π interaction, and ion exchange. Meanwhile, through regeneration tests, simulated wastewater treatment experiments, and cost calculations, it was found that BPB has great potential for practical applications. This work demonstrated that microwave-assisted pyrolysis is a viable low-cost approach for producing excellent sorbents from biomass, and banana peel is a promising feedstock to prepare biochar for dye removal.

Adsorption of Congo red dye in water by orange peel biochar modified with CTAB

In order to improve the adsorption effect of biochar on Congo red dye, this study used hexadecyl trimethyl ammonium bromide (CTAB) to organically modify orange peel biochar (OBC) to produce CTAB-modified orange peel biochar (NOBC), and the biochar before and after modification was analyzed by SEM-EDS, FTIR and BET. The adsorption performance of NOBC on Congo red dye was investigated and the adsorption mechanism was studied. The results showed that the adsorption amount was influenced by the initial concentration, adsorption time and solution pH. NOBC adsorbed 50 mg L^-1 CR with an equilibrium time of 60 min and an equilibrium amount of 290.1 mg g^-1, while the adsorption equilibrium time of OBC was 210 min and an equilibrium amount of 155.2 mg g^-1, the adsorption of CR by NOBC was above 210 mg g^-1 at pH 2 to 11, NOBC can be recycled three times. The experimental results showed that the adsorption data of CR on NOBC were consistent with the Langmuir isothermal adsorption model and the Pseudo-second-order model, and the mechanism of CR adsorption on NOBC mainly included electrostatic attraction and surface adsorption. In conclusion, NOBC is a promising material for dye wastewater adsorption.

A critical review on the development of lanthanum-engineered biochar for environmental applications

Biochar and lanthanum (La) have been widely used in environment. However, there is a lack of knowledge and perspective on the development of La-engineered biochar (LEB) for environmental applications. This review shows that LEBs with a variety of La species via pre-/post-doping routes are developed for environmental applications. Specifically, precipitation, gelation, and calcination are the common sub-processes involved in the pre-/post-doping of La on the resultant LEB. The dominant La species for LEBs is La(OH)₃, which is formed through precipitation of La ions with various bases. Various La carbonates, e.g., LaOHCO₃, La₂(CO₃)₃, La₂CO₅, and NaLa(CO₃)₂, are also involved in the preparation of LEBs. The LEBs are high-efficient in the adsorption of phosphate, arsenic, antimonate and fluoride ions, attributed to the strong affinity of La to oxyanions and Lewis hard base. Lanthanum is also favorable for co-doping with transition metal species to further enhance the performances in adsorption or catalysis. This review also analyzes the prospects and future challenges for the preparation and application of LEBs in environment. Finally, this review is beneficial to inspire new breakthroughs on the preparation and environmental application of LEBs.

Efficient removal of Tris(2-chloroethyl) phosphate by biochar derived from shrimp shell: Adsorption performance and mechanism study

Tris(2-chloroethyl) phosphate (TCEP) has been detected all over the world as a typical refractory organic phosphate, especially in groundwater. This work applied a calcium-rich biochar derived from shrimp shell as a low-cost adsorbent for TCEP removal. Based on the kinetics and isotherm studies, the adsorption of TCEP on biochar was monolayer adsorbed on a uniform surface, with SS1000 (the biochar was prepared at the carbonization temperature of 1000 °C) achieving the maximum adsorption capacity of 264.11 mg·g^-1. The prepared biochar demonstrated stable TCEP removal ability throughout a wide pH range, in the presence of co-existing anions, and in diverse water bodies. A rapid removal rate of TCEP was observed during the adsorption process. When the dosage of SS1000 was 0.2 g·L^-1, 95% of TCEP could be removed within the first 30 min. The mechanism analysis indicated that the calcium species and basic functional groups on the SS1000 surface were highly involved in the TCEP adsorption process.

Removal of Malachite Green using carbonized material derived from disposable facemasks: optimization of removal process through Box-Behnken design

Water resources are being heavily contaminated due to the huge load of toxic pollutants released by industrial activities. Among various physical and chemical methods, adsorption is considered as a promising method for rapidly removing contaminants from wastewater. In the present study, a novel carbon-based adsorbent was prepared through controlled pyrolysis of disposable facemasks. The properties of carbonized compound (CC) were characterized by FTIR, XRD, SEM and EDX. The pollutant removal efficiency of CC was initially investigated with synthetic dyes Malachite Green (MG) and Congo Red (CR). The peaks observed in FTIR spectra corresponding to C=O and C=C and C-N functional groups on adsorbed CC surface confirm the interaction between dye and CC. The XRD spectra of CC showed strong peaks at 2θ = 26.629, 27.488, 27.810 and 29.404 which correspond to the disordered graphitic plane. The SEM images of CC showed good porosity nature. A quadratic model was developed through response surface methodology by conducting a series of Box-Behnken design experiments. Adequacy of this model variables was ensured by ANOVA tests at P-value <0.05. The lower P-value (<0.0001) and higher F-value (44.54) of the quadratic model showed it was a significant model for dye removal. Finally, the optimal condition to obtain maximum MG removal (rate >99%) was identified by desirability function as CC 1000 and MG 212 mg/L and adsorption time 180 min. Adsorption kinetic study indicates that a pseudo second-order kinetic model showed the best fit with R²=  0.999.

A Critical Review of Snail Shell Material Modification for Applications in Wastewater Treatment

Sea material is becoming increasingly popular and widely used as an adsorbent in wastewater treatment. Snail shell, a low-cost and natural animal waste material, has been shown to have a high calcium content (>99%) and a large potential surface area for the development of sustainable adsorbents. This paper presents a novel synthesis of methods for using snail shell absorbent materials in the treatment of wastewater containing heavy metals, textile dyes, and other organic substances. Modified biochar made from snail shells has gained popularity in recent years due to its numerous benefits. This paper discusses and analyzes modification methods, including impregnating with supplements, combining other adsorbents, synthesis of hydroxyapatite, co-precipitation, and the sol-gel method. The analysis of factors influencing adsorption efficiency revealed that pH, contact time, temperature, initial concentration, and adsorbent dose all have a significant impact on the adsorption process. Future research directions are also discussed in this paper as a result of presenting challenges for current snail adsorbents.

Green calcium-based photocatalyst derived from waste marble powder for environmental sustainability: A review on synthesis and application in photocatalysis

Calcium, with its excellent adsorptive property and higher permissible limits in the environment, emerges as an effective wastewater treatment earth metal. Most of the catalysts, photocatalysts, and adsorbents reported in the literature have heavy metal complex, which creates a leaching problem. Majorly, precursors used for the synthesis of heterogeneous catalysts for wastewater treatment are costly. Therefore, the use of such precursors would be not suitable and feasible approach from an economic point of view. This review work is focused on giving an overview of the utilisation of calcium-based catalysts (adsorbents and photocatalyst) for the removal/degradation of various types of dye water pollutants and summarises the reported effects of calcium as a base on the removal efficiency of dopants. In this article, an extensive literature survey is presented on the various photocatalysts developed and the different syntheses involved in their preparation. As the utilisation of marble powder is a green sustainable approach, the scope of various calcium-based photocatalysts and their application is presented. This article also aims for the elementary and inclusive determination of the effect of introducing calcium as a base for different catalysts and adsorbents.

Ecofriendly and low-cost bio adsorbent for efficient removal of methylene blue from aqueous solution

A novel bio adsorbent was fabricated from turmeric, polyvinyl alcohol and carboxymethyl cellulose for MB dye removal. The physicochemical, antibacterial and biodegradable nature of the film was evaluated using scanning electron microscopy, optical microscopy, universal testing machine, water contact angle, thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, agar disc diffusion method and soil degradability. The inclusion of turmeric into PVA/CMC film improves the biodegradability, antibacterial activity and thermomechanical property of the films. PVA/CMC/TUR film displayed good MB adsorption capacity (q_e: 6.27 mg/g) and maximum dye adsorption (R%; 83%) and was achieved at initial dye concentration of 10 mg/L with contact time 170 min at room temperature. The adsorption data of MB on PVA/CMC/TUR film was evaluated using four models Langmuir, Freundlich, Temkin and D-R isotherms. The different kinetic of adsorption (pseudo-first order, pseudo-second order and intraparticle diffusion model) was also applied for adsorption of MB on the films. The experimental result suggests that PVA/CMC/TUR films are an alternate cheap adsorbent for water treatment.

Sustainable conversion of textile industry cotton waste into P-dopped biochar for removal of dyes from textile effluent and valorisation of spent biochar into soil conditioner towards circular economy

Effective immobilization of industrial waste into biochar development could be one of the most promising technologies for solid waste management to achieve circular economy. In this study, post-industrial cotton textile waste (PICTW), a cellulose rich industrial waste, was subjected to slow pyrolysis to develop a surface engineered biochar through phosphoric acid impregnation. Biochar produced at 500 °C designated as PICTWB500 showed a maximum methylene blue number (240 mg g^-1) with remarkable specific surface area of 1498 m² g^-1. FESEM, FTIR, XRD and Raman spectra analysis were performed to investigate the surface texture and functionalities developed in the biochar. Adsorption efficiency of the biochar was assessed using drimarene red, blue, violet, and black dyes as model dye pollutants in batch mode at different biochar dose, pH and contact time. The maximum monolayer adsorption capacity was obtained in the range 285-325 mg g^-1 for different dyes, determined from Langmuir adsorption model. The kinetic behaviour was more favourable with the pseudo second-order model. The recycling ability of PICTWB500 was proven to be effective up to 6th cycle without compromising its adsorption efficiency significantly. This study demonstrated an excellent adsorption capability of the biochar in dye laden real textile effluent and recycling of spent biochar as a precursor of bio compost. Hence, this study established a dual win strategy for waste utilization in textile industry using a closed loop approach with substantial techno-economic feasibility that may have potential applications.

State-of-the-art of research progress on adsorptive removal of fluoride-contaminated water using biochar-based materials: Practical feasibility through reusability and column transport studies

Fluoride (F^-) is one of the essential elements found in soil and water released from geogenic sources and several anthropogenic activities. Fluoride causes fluorosis, dental and skeletal growth problems, teeth mottling, and neurological damage due to prolonged consumption, affecting millions worldwide. Adsorption is an extensively implemented technique in water and wastewater treatment for fluoride, with significant potential due to efficiency, cost-effectiveness, ease of operation, and reusability. This review highlights the current state of knowledge for fluoride adsorption using biochar-based materials and the limitations of biochar for fluoride-contaminated groundwater and industrial wastewater treatment. Biochar materials have shown significant adsorption capacities for fluoride under the influence of low pH, biochar dose, initial concentration, temperature, and co-existing ions. Modified biochar possesses various functional groups (-OH, -CC, -C-O, -CONH, -C-OH, X-OH), in which enhanced hydroxyl (-OH) groups onto the surface plays a significant role in fluoride adsorption via electrostatic attraction and ion exchange. Regeneration and reusability of biochar sorbents need to be performed to a greater extent to improve removal efficiency and reusability in field conditions. Furthermore, the present investigation identifies the limitations of biochar materials in treating fluoride-contaminated drinking groundwater and industrial effluents. The fluoride removal using biochar-based materials at an industrial scale for understanding the practical feasibility is yet to be documented. This review work recommend the feasibility of biochar-based materials in column studies for fluoride remediation in the future.

A new type of calcium-rich biochars derived from spent mushroom substrates and their efficient adsorption properties for cationic dyes

Adsorption is commonly accepted as a most promising strategy in dye wastewater treatment, and the widespread use of adsorption emphasizes the need to explore low-cost but excellent adsorbents. Herein, a low-cost adsorbent (calcium-rich biochar) was developed, which was directly pyrolyzed from spent mushroom substate without any modification. This study evaluated the potential application of two calcium-rich biochars (GSBC and LSBC) derived from spent substrates of Ganoderma lucidum and Lentinus edodes, respectively. The effects of pyrolysis temperature on the calcium-rich biochars characteristics and their adsorption mechanism for cationic dyes (Malachite Green oxalate (MG) and Safranine T (ST)) were studied systematically. The increase in pyrolysis temperature from 350 to 750 °C led to an increase in both biochar ash, Ca content, and specific surface area, which made high-temperature biochars (GS750 and LS750) the superior adsorbents for cationic dyes. Batch adsorption results showed LS750 was more efficient to adsorb dyes than GS750 attributed to its higher Ca content and larger specific surface area. According to the Langmuir model, LS750 had high adsorption capacities of 9,388.04 and 3,871.48 mg g⁻¹ for Malachite green and ST, respectively. The adsorption mechanism of dye MG could be attributed to pore filling, hydrogen bonding, electrostatic interaction, ion exchange, and π-π stacking, while ST adsorption mainly involved pore filling, electrostatic interaction, ion exchange, and π-π stacking. Attributed to their excellent adsorption performance, cheap source, and good reusability, biochars obtained from SMSs were very promising in dyeing wastewater treatment.

Sustainable use of Ca(OH)2 modified biochar for phosphorus recovery and tetracycline removal from water

To prevent possible secondary pollution from phosphorus-loaded biochar (BC) in agricultural systems, this study investigated the sustainable use of Ca(OH)₂ modified wood biochars (Ca-BCs) for P recovery while significantly lowering the tetracycline (TC) adsorption onto Ca-BCs. Ca-BCs were prepared via calcination of mixtures of Ca(OH)₂ and wood BC under 100-500 °C for removing P and TC from water. Compared to the pristine BC (without Ca(OH)₂ modification), Ca-BC100 (Ca-BC prepared at 100 °C) showed a significant increase of P adsorption capacity from 4.00 to 138.70 mg/g due to reactive interaction between P and Ca(OH)₂ on Ca-BC while decrease of TC adsorption capacity from 62.17 to 20.86 mg/g owing to decrease of surface area from 260.50 to 120.26 m²/g. Batch adsorption tests implied that the P adsorption on Ca-BC100 would occur mainly via electrostatic attraction (pH > 2.1) and formation of hydroxylapatite (Ca₅(PO₄)₃(OH)) between phosphate and Ca(OH)₂. In addition, Ca-BC100 reacted with TC via electrostatic attraction (pH > 7.6), complexation, hydrogen bond, and π-π interactions. P and TC adsorption onto Ca-BC100 was a chemical, endothermic, and spontaneous process. The dynamic adsorption experiments using a fixed bed column filled with Ca-BC100 indicated that Ca-BC100 could continuously and effectively remove P and TC from water. Ca-BC100 also effectively lowered P and COD in the dairy wastewater. Under the environmentally relevant conditions, continuous treatment of water containing P and TC using the pristine BC followed by Ca-BC100 showed the pristine BC removed 96% of TC and only 6% of P from water while Ca-BC100 made high recovery of P (94% of P) with negligible TC. Therefore, Ca-BC100 could be used for effective recovery of P with negligible TC from wastewater, and then applied to agricultural systems as a sustainable and safe P-rich biofertilizer.

Microbial-assisted soil chromium immobilization through zinc and iron-enriched rice husk biochar

Soil chromium toxicity usually caused by the tannery effluent compromises the environment and causes serious health hazards. The microbial role in strengthening biochar for its soil chromium immobilization remains largely unknown. Hence, this study evaluated the effectiveness of zinc and iron-enriched rice husk biochar (ZnBC and FeBC) with microbial combinations to facilitate the chromium immobilization in sandy loam soil. We performed morphological and molecular characterization of fungal [Trichoderma harzianum (F1), Trichoderma viride (F2)] and bacterial [Pseudomonas fluorescence (B1), Bacillus subtilis (B2)] species before their application as soil ameliorants. There were twenty-five treatments having ZnBC and FeBC @ 1.5 and 3% inoculated with bacterial and fungal isolates parallel to wastewater in triplicates. The soil analyses were conducted in three intervals each after 20, 30, and 40 days. The combination of FeBC 3%+F2 reduced the soil DTPA-extractable chromium by 96.8% after 40 days of incubation (DAI) relative to wastewater. Similarly, 92.81% reduction in chromium concentration was achieved through ZnBC 3%+B1 after 40 DAI compared to wastewater. Under the respective treatments, soil Cr(VI) retention trend increased with time such as 40 > 30 > 20 DAI. Langmuir adsorption isotherm verified the highest chromium adsorption capacity (41.6 mg g⁻¹) with FeBC 3% at 40 DAI. Likewise, principal component analysis (PCA) and heat map disclosed electrical conductivity-chromium positive, while cation exchange capacity-chromium and pH-organic matter negative correlations. PCA suggested the ZnBC-bacterial while FeBC-fungal combinations as effective Cr(VI) immobilizers with >70% data variance at 40 DAI. Overall, the study showed that microbes + ZnBC/FeBC resulted in low pH, high OM, and CEC, which ultimately played a role in maximum Cr(VI) adsorption from wastewater applied to the soil. The study also revealed the interrelation and alternations in soil dynamics with pollution control treatments. Based on primitive soil characteristics such as soil metal concentration, its acidity, and alkalinity, the selection criteria can be set for treatments application to regulate the soil properties. Additionally, FeBC with Trichoderma viride should be tested on the field scale to remediate the Cr(VI) toxicity.

Application of biochar as an innovative soil ameliorant in bioretention system for stormwater treatment: A review of performance and its influencing factors

As an emerging environment functional material, biochar has become a research hotspot in environmental fields because of its excellent ecological and environmental benefits. Recently, biochar has been used as an innovative soil ameliorant in bioretention systems (BRS) to effectively enhance pollutant removal efficiency for BRS. This paper summarizes and evaluates the performance and involved mechanisms of biochar amendment in BRS with respect to the removal of nutrients (TN (34-47.55%) and PO₄^3--P (47-99.8%)), heavy metals (25-100%), pathogenic microorganisms (Escherichia coli (30-98%)), and organic contaminants (77.2-100%). For biochar adsorption, the pseudo-second-order and Langmuir models are the most suitable kinetic and isothermal adsorption models, respectively. Furthermore, we analyzed and elucidated some factors that influence the pollutant removal performance of biochar-amended BRS, such as the types of biochar, the preparation process and physicochemical properties of biochar, the aging of biochar, the chemical modification of biochar, and the hydraulic loading, inflow concentration and drying-rewetting alternation of biochar-amended BRS. The high potential for recycling spent biochar in BRS as a soil ameliorant is proposed. Collectively, biochar can be used as an improved medium in BRS. This review provides a foundation for biochar selection in biochar-amended BRS. Future research and practical applications of biochar-amended BRS should focus on the long-term stability of treatment performances under field conditions, chemical modification with co-impregnated nanomaterials in biochar surface, and the durability, aging, and possible negative effects of biochar.

Degradation of methylene blue through Fenton-like reaction catalyzed by MoS2-doped sodium alginate/Fe hydrogel

In this study, a low-cost and high-performance MoS₂/sodium alginate (SA)/Fe (MSF) hydrogel catalyst was prepared. It was found that the MSF hydrogel could efficiently catalyze the degradation of methylene blue (MB) through the Fenton reaction without the addition of Fe²⁺. The reaction was initiated by Fe²⁺ which was derived from the cyclic redox reaction between MoS₂ and Fe³⁺ and produced large quantities of ·OH to degrade the MB. The effect of MoS₂ concentration, FeCl₃·6H₂O concentration, H₂O₂ dosage, solution pH, and light on the degradation was systematically studied. The MoS₂ concentration of 0.5 mg/ mL, FeCl₃·6H₂O concentration of 0.25 g/mL, 50 μL H₂O₂, and the pH of 4.0 were the optimized parameters. Moreover, it was found that the MB degraded faster under the infrared radiation. The MB removal rate reached as high as 98% within 15 min in the presence of a low concentration of H₂O₂ and the procedure could be repeated 5 times. The MSF hydrogel provided an effective and simple strategy for the sustainable degradation of organic pollutants in wastewater.

Recent advances in biochar technology for textile dyes wastewater remediation: A review

With the continuous rise of industrialization and agriculture, the concentration of organic contaminants such as dyes in the ecosystem has increased in subsequent years, causing major environmental contamination. Adsorption has been revealed to be a reliable and cost-effective way of eliminating organic pollutants. Biochar technology has the potential of converting trash into treasure when utilized for environmental remediation since it has numerous benefits such as the availability of diverse types of raw materials, low cost, and reusability. The potential of biochar as an adsorbent, support for catalysis, and a composite catalyst for dye degradation and mineralization is summarized in this research. It discusses its current research status in the adsorption and degradation of various dyes, incorporates the pertinent adsorption variables, encapsulates its regeneration techniques, investigates its engineering applications, and finally analyses limitations and discusses future development prospects.

A Review of the Removal of Dyestuffs from Effluents onto Biochar

The study provides a review of various applications of biomass-derived biochars, waste-derived biochars, and modified biochars as adsorbent materials for removing dyestuff from process effluents. Processing significant amounts of dye effluent discharges into receiving waters can supply major benefits to countries which are affected by the water crisis and anticipated future stress in many areas in the world. When compared to most conventional adsorbents, biochars can provide an economically attractive solution. In comparison to many other textile effluent treatment processes, adsorption technology provides an economic, easily managed, and highly effective treatment option. Several tabulated data values are provided that summarize the main characteristics of various biochar adsorbents according to their ability to remove dyestuffs from wastewaters.

Adsorptive removal of organic dyes via porous materials for wastewater treatment in recent decades: A review on species, mechanisms and perspectives

Organic dyes, a type of high toxic and carcinogenic chemicals that present severe threats to human and aquatic life, are the most commonly seen organic pollutants in wastewater of industries such as textile, rubber, cosmetic industry etc. Various techniques for the removal of dyes are compared in this review. Adsorption has proven to be a facile and promising approach for the removal of dyes in wastewater. This work focuses on the latest development of various porous materials for the adsorption of organic dyes. The characteristics, functionalization and modification of different porous materials are also presented. Furthermore, adsorption behaviors and mechanism of these adsorbents in the adsorption of organic dyes are critically reviewed. Finally, challenges and opportunities for future research in the development of novel materials for the highly efficient removal of dyes are proposed.

A sustainable natural clam shell derived photocatalyst for the effective adsorption and photodegradation of organic dyes

In response to an increasing desire for modern industries to be both green and sustainable, there has been increasing research focus on the reutilization of natural waste materials to effectively remove and degrade toxic wastewater effluents. One interesting food industry waste product is clam shell. Here a new photocatalytic nanomaterial derived from marine clam shells was successfully prepared and characterized. Thereafter the material was applied for the removal of two target dyes from aqueous solution, where the effect of both catalyst dose and initial dye concentration on adsorption and photocatalysis was investigated. The maximum adsorption capacities of methylene blue (100 mg/L) and Congo red (500 mg/L) were 123.45 mg/g and 679.91 mg/g, respectively, where adsorption followed pseudo second order kinetics predominantly via a chemical adsorption process. The photodegradation removal efficiencies of the two dye solutions under visible light irradiation were 99.6% and 83.3% for MB and CR, respectively. The excellent degradation performance in a mixed dye solution, with strong degradation capability and low cost, demonstrated that the clam shell catalyst material was a good candidate for practical field remediation of dye contaminated wastewater.

Biochar from Wood Chips and Corn Cobs for Adsorption of Thioflavin T and Erythrosine B

Biochars from wood chips (WC) and corn cobs (CC) were prepared by slow pyrolysis and used for sorption separation of erythrosine B (EB) and thioflavin T (TT) in batch experiments. Biochar-based adsorbents were extensively characterized using FTIR, XRD, SEM-EDX, and XPS techniques. The kinetics studies revealed that adsorption on external surfaces was the rate-limiting step for the removal of TT on both WC and CC biochar, while intraparticle diffusion was the rate-limiting step for the adsorption of EB. Maximal experimental adsorption capacities Qmaxexp of TT reached 182 ± 5 (WC) and 45 ± 2 mg g-1 (CC), and EB 12.7 ± 0.9 (WC) and 1.5 ± 0.4 mg g-1 (CC), respectively, thereby indicating a higher affinity of biochars for TT. The adsorption mechanism was found to be associated with π-π interaction, hydrogen bonding, and pore filling. Application of the innovative dynamic approach based on fast-field-cycling NMR relaxometry indicates that variations in the retention of water-soluble dyes could be explained by distinct water dynamics in the porous structures of WC and CC. The obtained results suggest that studied biochars will be more effective in adsorbing of cationic than anionic dyes from contaminated effluents.

Dye adsorption of aluminium- and zirconium-based metal organic frameworks with azobenzene dicarboxylate linkers

The high efficiency of metal-organic-frameworks (MOFs) such as the ZIF, MIL and UiO type species in dye adsorption is well established. Recently, an emerging class of photoresponsive azobenzene-based MOFs has found suitable application in gas adsorption. However, there is a dearth of research on their use in the adsorption of dyes and other water pollutants. In this research, two microporous photoresponsive azobenzene dicarboxylate MOFs of Al³⁺ (Al-AZB) and Zr⁴⁺ (Zr-AZB) were synthesized for the adsorption of congo red (CR) dye. The surface and textural properties of the synthesized MOFs were characterized by FTIR, PXRD, SEM, TGA, BET and pore analysis. Both MOFs were crystalline, thermally stable up to 300 °C and stable in aqueous medium at room temperature. The Al-AZB displayed a higher surface area (2718 m²/g) than the Zr-AZB (1098 m²/g), which significantly impacted the higher adsorption of CR. Besides, pore volumes of 0.86 cm³/g and 0.35 cm³/g were obtained for Al-AZB and Zr-AZB, respectively. The maximum adsorption capacity of Al-AZB and Zr-AZB was 456.6 mg/g and 128.9 mg/g, respectively, with the former superior to other potent adsorbents. The pseudo-second-order and Langmuir models were well correlated with the dye uptake on the MOFs. Thermodynamics revealed random and endothermic sorption of CR dominated by chemisorption, while efficient regeneration and reuse of both MOFs were achieved using dimethylformamide as eluent. The results proved the potency of the synthesized photoresponsive MOFs, as highly efficient and reusable materials for dye adsorption.

Chitin-biocalcium as a novel superior composite for ciprofloxacin removal: Synergism of adsorption and flocculation

The ubiquitous present antibiotics in aquatic environment is attracting increasing concern due to the dual problems of bioaccumulation toxicity and antibiotic resistance. In this study, a low-cost chitin-biocalcium (CC) composite was developed by a facile alkali activation process from shell waste for typical antibiotics ciprofloxacin (CIP) removal. Response surface methodology (RSM) was utilized to optimize synthesis methodology. The optimized CC products featured superior CIP removal capacity of 2432 mg/g at 25 °C (adsorption combined with flocculation), rapid adsorption kinetics, high removal efficiency (95.58%) and wide pH adaptability (under pH range 4.0-10.0). The functional groups in chitin and high content of biocalcium (Ca²⁺) endowed CC abundant active sites. The kinetic experimental data was fitted well by pseudo-second-order and intraparticle diffusion model at different concentrations, revealing the removal was controlled by chemisorption and mass transport step. From the macroscopic aspect, flocs were produced with the increase of CIP concentration during the reaction, adsorption combined with flocculation were related to the CIP removal. From the microcosmic aspect, the superior removal performance was attributed to cation bridging, cation complexation among biocalcium-CIP and hydrogen bond between functional groups of chitin and CIP.

A state-of-the-art review on producing engineered biochar from shellfish waste and its application in aquaculture wastewater treatment

Global production of shellfish aquaculture is steadily increasing owing to the growing market demands for shellfish. The intensification of shellfish aquaculture to maximize production rate has led to increased generation of aquaculture waste streams, particularly the effluents and shellfish wastes. If not effectively managed, these wastes could pose serious threats to human health and the ecosystem while compromising the overall sustainability of the industry. The present work comprehensively reviews the source, composition, and environmental implications of shellfish wastes and aquaculture wastewater. Moreover, recent advancements in the valorization of shellfish wastes into value-added biochar via emerging thermochemical and modification techniques are scrutinized. The utilization of the produced biochar in removing emerging pollutants from aquaculture wastewater is also discussed. It was revealed that shellfish waste-derived biochar exhibits relatively higher adsorption capacities (300-1500 mg/g) compared to lignocellulose biochar (<200 mg/g). The shellfish waste-derived biochar can be effectively employed for the removal of various contaminants such as antibiotics, heavy metals, and excessive nutrients from aquaculture wastewater. Finally, future research priorities and challenges faced to improve the sustainability of the shellfish aquaculture industry to effectively support global food security are elaborated. This review envisages that future studies should focus on the biorefinery concept to extract more useful compounds (e.g., carotenoid, chitin) from shellfish wastes for promoting environmental-friendly aquaculture.

Removal of copper from sulfate solutions using biochar derived from crab processing by-product

Increasing metal demand is accelerating the mining and processing of minerals, however to ensure sustainable growth innovative approaches are required to better manage associated effluents. Biochar from the fast pyrolysis of residues from fishery and forestry operations has been studied as a low-cost, environmentally and economically friendly method for treating mine tailings and processing effluents. However, the bulk of the studies focus on terrestrial biomass (e.g. wood) and do not include potential inhibition/enhancement of adsorption due to pH controlling compounds. In this work biochar generated from snow crab (Chionoecetes Opilio) processing was studied as an adsorbent for copper solutions containing sulfate (a key compound in sulfide ore mining waters) with the objective of assessing adsorption capacity and the impact of sulfate on copper adsorption. The biochar, a porous structure comprised of calcite (CaCO₃), was alkaline and has a negative zeta potential under neutral and basic conditions. The crab biochar removed over 99% of Cu²⁺ from a 100 mg/L solution (sourced as CuSO₄) at a dosage of 5 g/L, which was higher than lignocellulosic biochar at the same biochar dosage. While metal adsorption can often be impacted at acidic conditions, Cu²⁺ adsorption was not impacted by initial acidic pH due to the biochar's buffering capacity. The Pseudo-Second Order (PSO) model fit the adsorption rate with maximum adsorption achieved in approximately 2 h. The maximum adsorption isotherm capacity was 184.8 ± 10.2 mg/g for Cu²⁺, much higher than existing commercial activated carbons and previously studied lignocellulosic biochars and followed the Freundlich isotherm. The adsorption mechanism responsible for removal of Cu²⁺ was found to be precipitation, in the form of the mineral posnjakite (Cu₄[(OH)₆SO₄]·H₂O). These results indicate for the first time that crab-based biochars are capable of adsorbing large quantities of Cu²⁺ from sulfate-rich solution, while also buffering solution pH, demonstrating promise as an acid mine drainage treatment for removal of harmful metals and reduction of acidity.

Preparation and characterization of magnetic modified bone charcoal for removing Cu2+ ions from industrial and mining wastewater

Heavy metal water pollution is an urgent global problem to be addressed. Copper ions are common toxic heavy metal pollutants in wastewater. In order to remove the excessive copper ions in wastewater, in this study, chicken bone charcoal was modified by sodium dodecyl sulfonate and combined with magnetic nanoparticles prepared with ferric chloride hexahydrate and ferrous sulfate heptahydrate to produce a high efficiency adsorbent. The characterization of the magnetically modified bone charcoal was analyzed by scanning electron microscopy, surface and porosity analyses, FTIR and thermogravimetric analysis. The optimal adsorption conditions of magnetically modified bone charcoal for Cu²⁺ were obtained through batch experiments. The highest removal rate and adsorption capacity of Cu²⁺ was 99.98% and 15.057 mg/g, respectively, when the pH was 3.0, adsorbent dosage was 0.2 g, initial concentration of the Cu²⁺ solution was 50 mg/L, and temperature was 25 °C. The adsorption process fitted well with the Langmuir isotherm and the pseudo-second-order kinetic model. The regeneration experiment indicated that M-SDS-BC-500 maintained a high removal rate after five repetitions. The results suggest that the adsorbent has wide application prospects.